The largest supercomputer in the world may be a top secret, as the specs of U.S. spy agencies are classified. Nonetheless top U.S. spy is publicly seeking help to build superconducting computers, which may offer the best path to exascale.

WASHINGTON -- The largest supercomputer in the world may be a top secret.

It might well be a system operated by the National Security Agency for sifting through telephone numbers, plain language text and images for terrorists. They spy agency's systems are classified, so no one knows just how big or fast they are.

But while intelligence agencies may not say what they have, they will say what they want.

The U.S. wants superconducting supercomputers, which may turn out to be the best path for a push to develop exascale systems, which would be about 1,000 faster than today's petaflop system.

That's the case made by the Director of National Intelligence in a published notice last week seeking help to develop superconducting systems. Such a system, "offers an attractive low-power alternative" to current systems.

The goal of the government's solicitation is "to demonstrate a small-scale computer based on superconducting logic and cryogenic memory that is energy efficient, scalable, and able to solve interesting problems."

To put the power problem in perspective, the largest U.S. supercomputer, Titan, uses just over 8 MW to reach 17.59 petaflops. A petaflop system would need significantly more power.

The U.S. believes superconducting technologies can reduce power demand for one petaflop to 25 kW or even 100 petaflops for about 200 kW, including the cost of cryogenic refrigeration. (1,000 kilowatts equals one megawatt).

Superconducting supercomputing uses super cold temperatures to get metal to a state where there is no or little resistance to electrical current.

"One simply cannot beat zero resistance, not that we know of now anyway," said Retief Gerber, the founder and director of NioCAD, a South African based firm that is working on superconducting technologies.

"Keeping superconductive electronics cold is like keeping a block of ice frozen in the freezer," said Gerber, "Once it's frozen one needs a lot less energy to keep it frozen.

"Keeping conventional electronics cool is like trying to keep a glass of water that's inside an oven, that's inside a fridge, cool," said Gerber.

Commercial coolers are available to sustain the very low temperatures, around -450 degree Fahrenheit, required for superconducting, and the operation of Josephson junctions, switches, that dissipate little energy.

The NSA, in particular, has had a long interest in superconducting technology, but "significant technical obstacles prevented exploration of superconducting computing," the government said in its solicitation. Those innovations include cryogenic memory designs that allow operation of memory and logic in close proximity within the cold environment, as well as much faster switching speeds.

Gerber has written that superconducting electronics have improved over the last two decades to the point where complex circuits can be operated at clock frequencies surpassing 100 GHz.

The budgets of U.S. intelligence agencies aren't disclosed, but they clearly need energy efficient computers.

The NSA is building a one million square foot, $1.2 billion data center in Utah. It will have the capacity to support 65 MW, which includes the power needed for the entire facility, not just its computers.

The world's fastest system, China's 33.86 petaflop Tianhe-2, has a peak power load of 16.7 MW, and uses 24 MW when cooling is added. That's a major share of a power plant's output.

Conventional computing systems, and their normal metal interconnects, "appear to have no path to be able to increase energy efficiency fast enough to keep up with increasing demands for computation," the government said.

Patrick Thibodeau covers SaaS and enterprise applications, outsourcing, government IT policies, data centers and IT workforce issues for Computerworld. Follow Patrick on Twitter at @DCgov, or subscribe to Patrick's RSS feed . His email address is pthibodeau@computerworld.com.